In any dual xy-axis rotation rate gyroscope, it is desirable to minimize the cross-talk sensitivity between the two sensitive axes. This implies that, for example, for xy-axis rotation-rate gyroscopes, the sensitivity to x-axis rate should be decoupled from the sensitivity to y-axis rate when both x-axis and y-axis rates are applied to the gyroscope simultaneously. This can be achieved either by isolating the two sense modes mechanically or employing some compensation method with electronics. The former method will increase the form factor of the device and the latter makes the circuit very complex. This problem is more challenging for xy-axis gyroscopes in comparison with xz-axis or yz-axis gyros since in the xy-axis gyroscope, both sensitive axes are in-plane.
One technique for reducing cross-talk sensitivity in xy-axis shell-type gyroscopes is to drive the shell-type gyroscope in an out-of-plane mode and sense the Coriolis forces using two in-plane modes. Here, the drive forces are perpendicular to the plane of the gyroscope, which produces velocities along the z-axis. Due to the application of simultaneous in-plane rotation rates around x-axis and y-axis, the device will be sensitive to both rates, and Coriolis forces will be created along both the y-axis and the x-axis at any single point, respectively. To reduce this cross-talk sensitivity between the two modes, mode rejection and calibration methods are typically implemented. In addition, a set of electrodes is typically dedicated to distinguish sensing x-axis rotation rates from y-axis rates, which consumes more space and results in more complicated MEMS structure and routings as well as associated circuitry.